"I think there are naive investors with no discipline, throwing out term sheets at nine figures right now, with no diligence," Sacca told Emily Chang in an interview with Bloomberg TV. "Well, if you really look at this thing, it's not gonna be a two-horse race. Lyft doesn't survive. And Travis is never gonna buy it."

Lyft raised $150 million in May at a reported $2.5 billion valuation for the company. Icahn was responsible for $100 million in the round.

"I think he made a big mistake," Sacca said in an interview with Bloomberg's Emily Chang. "This is a winner take all game. And Travis will take all."

It's not a big surprise for Sacca to back Uber over its competitor. Sacca reportedly owns at least 4% of the company's shares — although he told Bloomberg that's not why he would never buy Lyft shares.